U.S. Marines and soldiers uncover roadside bombs hidden underneath a pile of boulders in the courtyard of a large Sunni mosque in Haditha

U.S. military officials says they have completed a major sweep of western Iraq aimed at suppressing militant attacks in the lead-up to next week's constitutional referendum.

A spokesman in Baghdad Friday said U.S.-led troops killed 50 insurgents during the six-day operation along the Syrian border. He also said six U.S. Marines were killed by two separate roadside bombs in the area of operations.

The end of the military offensive comes just over one week before Iraqis go to the polls to vote on the country's new constitution. Shi'ite and Kurdish leaders support the constitution, while many Sunnis have denounced it.

Meanwhile, Iraqi President Jalal Talabani told a British television network, Sky News, Iraqi forces will not be ready to replace U.S.-led troops for two years. But he said coalition withdrawal depends on a resolution from the U.N. Security Council and negotiations between the Iraqi government and coalition forces.